KR0152449B1 - Diffuse secondary emission electron shower - Google Patents

Abstract

The present invention is directed to ion implantation characterized by an improved beam neutralizer. The cylindrical electron source surrounds the ion beam at the position before the ion beam enters the injection chamber. The regularly spaced cavity of the electron source contains wire filaments which energize and emit electrons. Electrons are accelerated through the region of the ion beam and collide with the walls facing inwardly of the cylindrical electron support. This neutralizes the ion beam and emits low energy electrons. By performing the ionizing gas into the region between the electron emitting surface and the ion beam, the performance of the non-neutralizer is improved.

Description

Diffused secondary emission

1 is a schematic view of an injection device.

2 is a cross-sectional view of the ion implanter showing the ion beam path from the ion source to the ion implantation chamber.

3 is a cross-sectional view of an ion implanter showing a beam neutralizer for injecting low energy electrons into an ion beam.

3A is a plan view taken along line 3A-3A in FIG.

3B is a plan view taken along line 3B-3B of FIG.

4 is a cross-sectional view of a cylindrical support used for multifilament illustrating the inward facing secondary electron emission surface.

5 is an enlarged plan view of a filament that directs high energy electrons to the area of the non-neutralizer.

6 is a schematic diagram of a non-integrator showing secondary electron generation from high-energy primary electrons emitted from multiple equally spaced filaments.

* Explanation of symbols for main parts of the drawings

12: ion source 14: decomposed magnet

22: ion implantation room 40: support

116,118,120 Battery 110 Faraday Cup

150: neutralizer 160: filament

166: insulator 270, 272: nut

274: spring

The present invention relates to ion implanters, in particular ion beam neutralizers for ion implanters. Ion implanters are used to fabricate semiconductors by doping silicon wafers. Impurities used to dope the wafer are ionized to form an ion beam, which is then used to dope the silicon wafer by impinging the ion beam onto the wafer. One problem that arises in implantation doping systems is wafer charging. When the ion beam is in direct contact with the wafer, the wafer charge hits the wafer surface with positively charged ions.

Charging is usually uneven and can generate many electric fields that can damage the wafer, making it unsuitable for use as a semiconductor material.

In a conventional injection system, an electron shower device was used to neutralize the space charge in the ion beam. Conventional electronic shower devices utilize secondary electron emission caused when energy electrons strike a metal surface.

Low-energy electrons from the metal plane directly block the ion beam or collide directly with the wafer plane and directly neutralize the wafer.

The current density of electrons obtained by secondary emission from the metal surface is limited by the potential difference between the ion beam and the emission surface.

As the non-potential is lowered due to very good neutralization, the secondary discharge electron current evicted from the emission side decreases.

In the case of a charged ion beam directly on an isolated wafer, the electron current must be equal to the ion beam current to prevent the neutralizer from charging the wafer.

When the beam current is initially low, the wafer is charged until the ion beam potential is sufficient to extract the required amount of electron current from the secondary emission surface.

Low-potential ions do not mean that no wafer charge occurs because the center of the beam becomes positive and the outside of the beam becomes negative due to the connection of negative charges surrounding the ion beam.

In practice, the space charge on the metal electron emission side is partially neutralized by slowing ions from residual gas ionization along the ion beam path.

As a result, higher electron currents can be extracted than theoretically anticipated and in fact the prior art uses low current gas pressure to provide low energy electrons.

Farley's U.S. Patent No. 4,804,837 discloses a non-neutralizing device with a source of high energy electrons that is swept back and forth through a neutralization zone containing ionization gas.

As the high energy electrons pass through the neutralization zone, they neutralize the beam by ionizing the gas providing the low energy electrons.

It was published in Farray's' 837 patent and included there.

If the ion beam is not sufficiently neutralized, the ion beam will break or expand due to metal collision of positively charged ions in the beam.

To minimize this zone of destruction, an electromagnetic field is placed upstream from the residue shower.

Since a typical ion implantation chamber has a support for supporting a silicon wafer through an ion beam along a circular path, the wafer support is held at ground potential after the ion beam encounters the wafer, and the subsequent wafer is as described above.

As a result, whenever the wafer passes through the ion beam, the ion beam potential causes a sudden perturbation.

This fluctuation in beam current is reduced by providing a potential hole plate upstream of the non-neutralization region.

The use of compression apertures introduces two undesirable problems. This hole has the problem of boundary conditions causing sharp divergence of non-potential.

This can weaken ion beam breakdown downstream from the compression aperture.

In addition, the electric field in the region of the aperture can deflect electrons in the non-neutralizer located downstream of the injection chamber region.

This is undesirable because it creates a region of positive charge in the center core of the ion beam and a negative charge region around the outside of the ion beam.

In other words, the ion beam is neutralized in a broad sense, positive charge buildup occurs at the center of the wafer, and charge occurs outside.

This creates an undesirable electric field. The purpose of Perray's' 837 patent is to increase secondary electron production by increasing time-period electrons in the region of gas molecules where the ion beam collides.

The object of the present invention relates to an ion implanter for ion beam treatment of circular workpieces. Ion implanters are used to ion-dope silicon materials to create semiconductors. The source releases positively charged ions and forms an ion beam that treats the prototypical workpiece.

The beam forming apparatus includes a structure for forming an ion beam from ions when ions are present in the ion beam source.

Such a structure generally includes a cell that accelerates ions as well as a decomposing magnet that decomposes a large amount of ions to separate ions having undesirable masses and ions that are directly directed to the circular workpiece.

In ion implantation sites, i.e., in one or more circular workpieces, silicon wafers generally achieve the implanted dose through the ion beam.

Upstream of the injection site, the non-neutralizer directs low-energy electrons directly to the ion beam to prevent wafer charging by positively charged ion beams.

The non-neutralizer directs high-energy electrons and the metal member partially surrounding the ion beam providing the non-neutralized electrons in direct contact with the surface facing the inner side of the metal member so that low-energy neutralized electrons enter the region of the ion beam and reduce wafer charging. It includes a plurality of filaments.

An ion implanter made in accordance with a preferred embodiment of the present invention includes a cylindrical member forming an inwardly facing cylindrical electron emitting surface.

The filaments emitting high energy electrons are located in the cavity of the cylindrical member.

According to a preferred embodiment of the invention the cylindrical body extends the distance along the ion beam sufficient to achieve non-neutralization.

This is accomplished without a compressed cell, which, as mentioned above, produces undesirable results in prior art injectors.

FIG. 1 shows an ion implantation apparatus 10 having an ion source 12 and a beam decomposing magnet 14 contained within the high voltage housing 16.

Ion beam 20 exiting source 12 follows a controlled movement path in which housing 16 resides and enters ion implantation chamber 22.

An ion beam 20 is formed along the beam movement path from the source 12 to the injection chamber 12, and is accelerated by weakening with a potential drop from the ion injection chamber 16 of high voltage to the stationary injection chamber.

The decomposing magnet 14 approaches the ion implantation chamber 22 with ions having a suitable mass. The ion beam 20 passes through a high voltage insulating bushing 16 made of an electrical insulator that isolates the high voltage housing 16 and the high injection chamber 22 along the moving passage from the housing 16 to the injection chamber 12.

The ion implantation chamber 22 is supported on a moving pedestal 28.

This clears the injection chamber 22 with respect to the ion beam.

The ion beam collides with the wafer support 40 installed to rotate around the axis 42. Around the outer periphery of the wafer support 40, the wafer support 40 supports the multisilicon and moves these wafers along the circular path.

The ion beam 20 selectively dope these wafers with ionic impurities that block the circular wafer travel path and impinge the ions onto each wafer.

After the wafer is placed on the support, the motor 50 rotating the support 40 rotates the support 40 at high speed.

Additional details regarding the ion implantation apparatus are included in US Pat. No. 4,672,210 to Mr. Armstrong et al. This is included here for reference.

The silicon wafer is inserted into the ion implantation chamber 22 through the vacuum port 71 by the robot arm 70.

The ion implantation chamber 22 is vacuumed at a low pressure, such as the pressure along the ion beam path, by the vacuum pump 72.

Robert arm 70 moves the wafer back and forth between the cassettes 73 that accumulate the wafer.

Mechanisms for achieving this transfer are known in the prior art. An additional pump (not shown) vacuums the ions from the source 12 to the injection chamber 22. As can be seen in FIGS. 1 and 2, the ions escaping from the source 12 move to the decomposing magnet 14 along a straight path.

The source 12 includes a high density plasma chamber 76 having an elliptical escape hole.

Additional description of the source is disclosed in US Pat. No. 5,026,997 to Mr. Benveniste, which is incorporated herein by reference.

Ions are accelerated from the plasma chamber 76 by the electric field set by the extraction battery 80 located outside the extraction hole and enter the region of the decomposition magnet 14.

The decomposing magnet 14 generates a magnetic field that refracts ions having a suitable mass in the orbit. These ions escape the decomposition magnet 14 and are accelerated along the movement path to be introduced into the injection chamber 12.

The magnet yoke 82 is tied with field windings not shown in FIG.

The injection control circuit located in the high voltage housing 16 adjusts the magnetic field strength by controlling the current in the field winding of the magnet.

The source 12 generates ions with large friction with masses different from those for implantation ions. These undesirable ions are deflected by the decomposing magnet 14 but deviate from the orbit.

Heavy ions follow a large orbit and strike the target plate 86 attached to the magnet. The ions, which are lighter than the ions used for implantation, follow a compact radius orbit and strike the target plate 90. The target plates 86 and 90 tend to be heated by the impact of ions. Refrigerants that reduce heat are supplied through supports (not shown) for target plates 86 and 90.

Faradaycom 110 is located along the beam moving path downstream of the decomposition magnet (14). The Faraday cup 110 blocks ions and prevents ions from reaching the injection chamber 22. The Faraday cup 110 is used to detect the ion beam current while the beam is being set.

It is used to block ions during other time intervals when ion implantation stops, such as when the wafer is loaded or unloaded into the implant chamber 22.

After exiting the decomposed magnet 14, the quadrupole lens 112 located in front of the high voltage isolation bushing 26 focuses the ion beam 20.

The quadrupole lens 112 refracts ions in the ion beam 20 to focus the ion beam at right angles to the image point, similar to the focus effect of the convex lens having a light beam. Ions in the ion beam 20 that are not sufficiently refracted or focused by the quadrupole lens 112 escape from the ion beam and never reach the ion implantation chamber 12.

Ions reaching the region of image point 114 are accelerated by series cells 116, 118, 120 up to the desired final implantation energy.

During ion implantation, the Faraday cup 110 is removed from the ion beam passageway and the ion beam enters the neutralizer 150.

The non-neutralizer 150 minimizes the charge of the wafer in the injection chamber 22 by directing the low energy electrons at the same ratio as the ion beam current.

3, 3a, 3b and 4-6 illustrate a preferred embodiment of the deneuterizer 150 designed according to the present name.

6 outlines the operation of the deneuterizer.

In this description the non-neutralizer 150 is positioned relative to the ion beam 20 having a diameter R1.

The cylindrical surface S, which provides low energy secondary electrons to neutralize the ion beam, has a space radially outward from the ion beam.

Spaced out side (S) A plurality of elongated filaments 160 emit electrons in all directions. The curved reflector R redirects electrons moving away from the ion beam 20 through a gap G, accelerating the emitted electrons through the region of the high percent ion beam 20, the surface S ).

When high-energy electrons collide with plane S, low-energy secondary electron emission 161 is caused. The secondary electrons move from the electron emission surface S to the region of the ion beam to neutralize the ion beam.

The cylindrical electron emitting surface S extends about 10 inches along the ion beam. This length allows electron focusing (non-neutralizing current) per unit time, and the wafer rotates through the ion beam, thereby neutralizing the beam whether the ion beam potential will change rapidly.

Description of the preferred structure of the de-neutralizer 150 is as follows.

The ion implanter structure surrounding the ion beam movement path in the region of the neutralizer 150 is grounded.

The surface S is also grounded. The current through filament 160 is about 6 amps with the application of a direct current potential along each filament of 10 volts.

The reflector R is connected to the negative end of the filament 160 while maintaining a potential of -300 V DC relative to ground. Screwed connector 163 extends through support plate 164 supporting non-neutralizer 150 and engages a threaded hole in sidewall 162. De-neutralizer 150 may remove the ion implanter if necessary. Since the area where the ion beam passes through the injection chamber is evacuated, the connection between the plate 164 and the side wall 162 must be evacuated.

Insulator 166 electrically insulates plate 164 from sidewall 162.

Plate 164 electrically insulated from sidewall 162 allows sensing of neutralizer currents directly directed to the ion beam.

Two flanges 170 and 171 are attached to the plate 164 and the ion beam extends radially into the area.

The neutralizer body 174 forms a surface S and surrounds the ion beam movement path.

The neutralizer body is supported by axially spaced end plates 176, 177 attached to the flanges 170, 171 by means of screwed connectors (not shown).

4 shows a cross-sectional view of the neutralizer body 174. The body 174 forms a cavity 210 spaced under the load that places the electron-emitting filament 160.

The filament 160 is preferably tungsten wire 10 mm in diameter and extends the length of the neutralizer 150. They are arranged with a gap S on the radially open surface S of the ion beam 20. Each filament 160 is supported by a filament assembly 220.

Each assembly 220 includes a support plate 222 connected to the neutralizer body 174 by a screwed connector 224.

The filament mounting block 226 is connected to the support plate 222 by a sharpened connector 228.

The support block 226 supports the electron reflector R biased to the negative potential of the filament 160. This thermally releases electrons from the filaments and refracts them in the region of the ion beam from the electron reflector 230.

When the high-energy electrons collide with the plane when the electron-emitting surface strikes, the body 174 is heated because energy is transferred from the high-energy electrons.

For this reason, a refrigerant (preferably water) is provided through the multi-extension passage 240 extending parallel to the filament 160.

Refrigerant is provided through the inlet tube 241 to the fitting 242 that delivers the refrigerant to the passage 243 of the end wall 176.

The refrigerant is applied to the body in a direction parallel to the passage of the beam from the first passage 240a to the second end plate forming the arcuate reset 244 (FIG. 3b) that transfers the adjacent passage.

Since the refrigerant moves backward along the ion beam passage to the first end plate forming the arcuate resets 245 connecting the adjacent passages 248 with each other, the refrigerant flow direction is reversed. After moving along the winding route while absorbing heat from the body 174, the refrigerant traverses the next passage 240b and escapes the end plate 177 through the escape passage 246 formed in the end plate 177.

As shown in FIG. 3, fitting 247 and tubing 248 store heated refrigerant from an ion implanter to a heat exchanger (not shown).

If the low concentration of ionization gas, such as argon, is directly in the region of high energy electrons through the ion beam neutralizer 150 experiment, performance is improved.

The ionization by ionizing the ions partially neutralizes the negative space charge on the cylinder wall because the ions slow down.

This gas is delivered by tubing 250 extending through plate 164 and flange 178.

The tube 250 delivers gas to the neutralizer in a radial position, such as the discharge surface S of the body 174 of the entrance and exit of the neutralizer. The through passage mounted to the body 174 accumulates the gas delivery tubing 250.

5 is an enlarged view of the filament assembly 220 located in one cavity formed by the body 174.

The wire filament 160 shown in FIG. 5 extends through the central bore of two threaded studs 260 spaced from the reflector R by an electrical insulator 262.

The opposite end of the filament 160 is connected by clipping the electrical connectors 264 and 265 connected to an external power source for energizing the filament 160.

In a preferred embodiment of the present invention, each of the multiple filaments 160 spaced around the circumference of the ion beam is to an energy source by two annular buses 266, 267 having a diameter larger than the neutralizer body 174. It is connected in parallel and has a space in the end plates 176 and 177 by the insulators 268 and 269.

The filament is energized with a direct current voltage through which current heats the filament and thermally releases electrons. These electrons have an electrical potential of about DC-300 volts and are accelerated to plane S by the electric field in the neutralizer.

The outer surfaces of the two studs 260 and 261 are screwed so that the tensioning nuts 270 and 272 are screwed onto the studs 260 and 262.

A spring 274 is caught between the tensioning nuts 270 and 272 of the insulator 262.

By controlling the position of the tension nut 270, 272 along the stud can control the compression of the spring 274 to control the tension of the filament (160).

The power supply 280 (FIG. 1) energizes the filament 160 and the reflector R. As shown in FIG.

No feedback control is needed for current or voltage.

A power source is connected to the buses 266 and 267 and biases the reflector of DC-300 volts voltage to the grounding body 174 and applies a 10 volt signal along the parallel coupling filament 160.

Since the nonpotential changes during the operation of the injector, neutralization changes the current to neutralize the beam and minimize wafer charge.

Preferred embodiments of the invention have been described with specificity. Many modifications are possible without departing from the spirit and scope of the invention.

Claims (10)

(A) beam forming means and (c) ion beams comprising a structure for forming an ion beam from an ion beam source releasing a positively charged charge and an ion beam source with (b) ions used to treat the circular workpiece. (I) a cylindrical metal member enclosing an ion beam having an inwardly facing curved surface for providing non-neutralizing electrons; (E) non-neutralizing means comprising a plurality of filaments positioned so as to direct high-energy electrons into contact with the inner facing surface of the metal member and allowing the neutralized electrons to enter the region of the ion beam, and (e) a cylindrical metal member for a plurality of filaments. An ion implanter for ion beam treatment of the circular workpiece, characterized in that it comprises an electric biasing power supply means. The ion implanter of claim 1, wherein the filament comprises an extended wire filament extending parallel to the ion beam axis. 3. The method of claim 2 wherein the cylindrical metal member comprises a member body having a filament support cavity spaced regularly to position the wire filaments at regular intervals around the ion beam. Ion implanter. (A) Source means for generating positively charged ion beams and directing the ion beams along the beam travel path to be projected onto the circular workpieces; (B) Circular workpiece positioning means for placing the circular workpieces in the ion beams at the injection site; C) Electron generation means located in front of the beam injection path in front of the injection site and directing high energy electrons through the beam neutralization zone; and (d) High-edge electrons notifying the beam neutralization zone and providing low-energy secondary electrons within the non-beam neutralization zone. And (e) power source means for biasing the electron generating means with an electrical potential to the conducting means for accelerating electrons from the electron generating means to the conducting means. 5. The method of claim 4, wherein the electron generating means comprises a plurality of wire filaments that thermally emit electrons, the conducting means comprises a face facing inwardly with the cylindrical metal member and the power supply means is capable of dislocation along the plurality of wire filaments. Ion beam injection device characterized in that the supply. 6. The ion beam implanter of claim 5, further comprising a source of ionizing gas that provides a low energy ion to said region by directing it to an inner radial region of the face facing the gas inwardly. (A) a metal body having a passage sized to pass an ion beam through the metal body, the metal body maintained at a fixed electrical potential for the ion beam, and (b) ion beam movement through the metal body with a regular space (D) a support structure for installing the filament mechanically connected to a plurality of elongated transfer-emitting filament metal bodies oriented parallel to the direction and electrically isolated from the metal body, and (c) an ultra-fast body for the ion beam; (E) power means for biasing the electron-emitting filament with a negative potential relative to the body and applying a potential along the filament to set a current that heats the filament sufficiently to emit electrons, and (e) high-energy electrons from the filament Metal bodies, which generally include ion beams facing the cylindrical face to emit low energy electrons as they face the face Ion beam neutralizer comprising a. 8. The ion beam neutralizer of claim 7, wherein the metal body forms a passage for providing a refrigerant through the body to reduce heat generated by collision of high energy electrons with the cylindrical surface. 9. The ion beam neutralizer of claim 8, wherein the support structure comprises a structure for providing refrigerant to and from the metal body. 9. The ion beam neutralizer of claim 8, further comprising a gas source that directs the ionizing gas into a radially inner region of the cylindrical surface of the metal body.